Hydrogen atom in a high magnetic field.

The low-lying energy levels of a hydrogen atom in a uniformly strong magnetic field [ital B] ([ital B][lt]10[sup 10] G) are calculated in a simple perturbative variational approach which combines the spirit of the variational principle and the conventional perturbation method. The total Hamiltonian is separated into four parts: a one-dimensional hydrogen-atom system; a two-dimensional harmonic-oscillator system; a [ital z]-component angular-momentum operator; and a perturbation part which contains an undetermined variable parameter but is independent of [ital B]. The first three parts can be solved exactly. The variational parameter introduced in the Hamiltonian can be determined by requiring the energy-correction expansion to converge as fast as possible. It is found that our calculated ground-state energy is in good agreement with those obtained by the previous works that used the wave-function-expansion approach for high magnetic fields up to [gamma]=7 (i.e., 10[sup 10] G for atoms).